Missense mutations, both those evoked directly and those accumulated during evolutionary divergence, may affect the subunit binding sites of heteropolymeric enzymes as well as their active site. This project aims to exploit the opportunity provided by recombinant DNA methods to examine the function and response to regulation of genes controlling enzymes of the tryptophan synthetic pathway from one procaryote operating in the cytoplasm of a different, distantly related procaryote. Special attention will be devoted to gram-negative, aerobic bacteria belonging to the genera Pseudomonas and Rhizobium, for earlier work demonstrated that they have striking differences from each other and from the Enterobacteriaceae in chromosomal organization and regulation of the trp genes. The occurrence of effective heteropolymeric enzymes comprised of subunits from different widely divergent procaryotic species will be investigated. When ineffective complexes are formed, as may be expected in most cases, attempts will be made to improve them by selecting critical mutations in the subunit's structural genes. This work will also seek to establish the ubiquity of attenuation as a general mechanism of regulation of gene activity in procaryotes and to determine whether this regulatory mechanism is equally effective in native and foreign cytoplasm. The efficiency of trp promoter sequences in foreign cytoplasm will be measured, as well as the relative ease of improving their effectiveness by mutational alteration of the nucleotide sequence.